The transition from early to late adenovirus gene expression is likely to be a key event in determining the potential outcome of the virus-host interaction: transformation is a result of early gene action: late genes are not expressed in virus transformed cells, and host cells in which late virus transcription proceeds normally can rarely, if ever, be transformed. Thus, understanding of adenovirus gene regulation is essential for the understanding of this model system for virus-induced cancer. Temperature-sensitive (ts) mutants of adenovirus type 5 (Ad5) will be used to study the relationship between viral DNA replication and the control of the late viral gene expression. Use of the mutants and arabinosyl cytosine to reversibly inhibit DNA replication will enable the study of the switch from early to late viral transcription in a situation of increased synchrony, relative to that obtainable during normal infection by wild-type virus. Viral transcriptions will be studied by filter competition-hybridization and by liquid-phase hybridization to Ad5 DNA fragments generated by digestion with restriction endonucleases. The role of the virus DNA template in regulating transcription will be studied by superinfection experiments. The regulation of synthesis of the 71,000 MW DNA-binding protein will be studied in a ts mutant that overproduces the protein. Isolation of adenovirus regulatory mutants will be attempted by the application of specific selective technique. Promoter-like mutants will be sought among revertants of an "early" ts mutant. Mutants defective in late gene expression will be isolated by a negative procedure using chemical analogs to interfere with the synthesis of functional viral proteins.